Energy-free refrigeration door and method for making the same

ABSTRACT

The present invention provides a refrigeration door, and method for making the same, for controlling condensation, providing thermal insulation, with a desired amount of visible transmittance, without using electricity to heat the door. The energy-free refrigeration door of the present invention includes a door frame housing and an insulating glass unit comprising inner, middle and outer sheets of glass. A first sealant assembly disposed around the periphery of the inner and middle sheets of glass forms a first chamber between the inner and middle sheets of glass. A second sealant assembly disposed around the periphery of the middle and outer sheets of glass forms a second chamber between the middle and outer sheets of glass. A gas, such as krypton, air, or argon is held in the first and second chambers. The outer sheet of glass and inner sheet of glass each have an unexposed surface that faces the middle sheet of glass. A low emissivity coating is disposed on the unexposed surfaces of the inner and outer sheets of glass so that the glass door as a whole has a U value that prevents formation of condensation on the outer surface of the outer sheet of the glass door, without the application of electricity to heat the door, while also providing the desired evaporation rate of condensation from the inner side of the inner sheet of the glass door.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates, generally, to refrigeration doorsand, in particular, to an energy-free refrigeration door providingcondensation control, thermal insulation, and a desired amount ofvisible transmittance. More particularly, the refrigeration door of thepresent invention achieves these desired characteristics through theapplication of a low-emissivity coating, without electrically heatingthe door. Throughout this application the term “refrigeration door” ismeant to refer to a door used for freezers, refrigerators and similarunits and cabinets. In addition, for purposes of this application theterm “energy-free” (as in energy-free refrigeration door) means thatelectricity is not applied to the glass to heat the glass.

[0003] 2. Discussion of the Background

[0004] Refrigeration doors for commercial freezers, refrigerators andthe like are typically constructed of glass to allow the customer toview the products placed therein for sale without opening the door.However, when condensation forms on the glass (sometimes referred to as“fogging”), the customer is not able to see through the door to identifythe products inside, which is undesirable from the standpoint of thecustomer and the store owner or retailer as well.

[0005] Moisture condenses on the outside of the glass refrigeration doorbecause the surface temperature of the outside of the glass is reducedbelow the ambient temperature in the store by the colder refrigeratedinterior of the freezer or refrigerator. When the temperature of thesurface of the glass drops below the dew point of the air in the store,moisture condenses on the surface of the glass. In addition, when a dooris opened in a humid environment, the innermost sheet of glass, whichforms the inside of the door, is also momentarily exposed to the ambientair of the store and condensation may form on the inside of the door aswell. The condensation on the inside of the glass door also occursbecause the temperature of the inside of the glass door is below the dewpoint of the ambient store air to which it is exposed.

[0006] As previously indicated, condensation on the glass door, whichmay become frost, prevents the customer from seeing the products forsale through the glass door. Consequently, when condensation or frost ison the glass door, the customer must perform the unpleasant task ofopening the refrigeration door to identify the contents inside, which isimpractical in a store with a large number of freezers or refrigerators.Not only is opening every refrigeration door tedious and time consumingfrom the customer's perspective, it is undesirable from the retailer'sstandpoint as well since it significantly increases the energyconsumption of the retailer's freezers and refrigerators, therebyresulting in higher energy costs to the retailer.

[0007] There are various industry performance standards whichrefrigeration doors are required to comply with in order to beacceptable. In the United States, much of the industry requires freezerdoors (but not refrigerator doors) that prevent external condensationwhen used in an environment with an outside temperature of eightydegrees Fahrenheit (80° F.), an outside relative humidity of sixtypercent (60%), and an inside temperature of minus forty degreesFahrenheit (−40° F.). Other countries have different requirements.

[0008] As is well known in the art, a typical refrigeration door iscomprised of an insulating glass unit (IGU) housed in a door frame. TheIGU in a refrigeration door is, typically, comprised of two or threesheets of glass sealed at their peripheral edges by a sealant assembly,generally referred to as an edge seal. In an IGU comprised of threesheets of glass, two insulating chambers are formed between the threesheets of glass. In an IGU comprised of two sheets of glass, a singleinsulating chamber is formed. Typically, IGUs for refrigerators areconstructed of two sheets of glass, while IGUs for freezers employ threesheets of glass. Once sealed, the chambers are often filled with aninert gas such as argon, krypton, or other suitable gas to improve thethermal performance of the IGU.

[0009] Most conventional approaches to preventing or reducingcondensation in a refrigeration door involve supplying energy to thedoor by including a conductive coating on one or more of the glasssurfaces of the IGU for electrically heating the glass. The purpose ofheating the glass is to maintain the temperature of the glass above thedew point of the warmer ambient air of the store. By heating the glassabove the dew point, the undesirable condensation and frost areprevented from forming on the glass in the door, providing a clear viewthrough the glass to the interior of the refrigeration compartment.

[0010] In a door consisting of a three-paned IGU, an unexposed surfaceof one or two of the sheets of glass is coated with a conductivematerial. The conductive coating is connected to a power supply by twobus bars or other electrical connectors mounted on opposite edges of theglass. As current passes through the coating, the coating heats, therebyheating the glass sheet to provide a condensation-free surface. Thecoating on the IGU of a refrigeration door is normally applied to theunexposed surface of the outermost glass sheet. However, becausecondensation sometimes forms on the inside of the inner sheet of glass,the unexposed surface of the innermost sheet of glass may also be coatedfor heating to prevent condensation.

[0011] There are numerous drawbacks and problems associated with theseconventional heated refrigeration doors of the prior art. First, heatingthe door incurs an energy cost above and beyond the energy costs of thecooling system. In a standard size commercial freezer, the additionalcost to heat a freezer door is substantial—based on current electricalutility pricing, such additional costs can be $100 per year or more foreach freezer. Considering that many stores utilize multiple freezers,with some supermarkets and other food retailers utilizing hundreds offreezers, the cumulative energy costs associated with such heatedfreezer doors are significant.

[0012] Second, excess heat from conventional heated refrigeration doorswill migrate to the refrigeration compartment, creating an additionalburden on the cooling system, which results in still greater energycosts. Third, if the power supplied to the door for heating is too low,is turned off, or is shut down due to a power outage, condensationand/or frost will form on the glass. If the power dissipation is toohigh, unnecessary additional energy costs will be incurred. In order toreduce the occurrence of these problems, such heated glass doors oftenrequire precise control of the door heating system. In order to achievethe necessary precise control of the door heating system, an electricalcontrol system is required, which results in increased design andmanufacturing costs, as well as substantial operational and maintenancecosts.

[0013] Fourth, these electrically heated glass doors present a safetyhazard to customers and a potential risk of liability and exposure toretailers and refrigeration system manufacturers. The voltage applied tothe glass door coating is typically 115 volts AC. The shopping cartsused by customers in stores are heavy and metal. If the shopping cartstrikes and breaks the glass door, electricity may be conducted throughthe cart to the customer, which could cause serious injury or evendeath.

[0014] U.S. Pat. No. 5,852,284 and U.S. Pat. No. 6,148,563 discloseapplying a voltage to a glass coated with a conductive coating (whichmay be a low emissivity coating) to control the formation ofcondensation on the outer surface of the glass door. The conductivecoating, such as a low emissivity coating, provides a resistance to theelectricity, which produces heat, while also providing desirable thermalcharacteristics. However, the refrigeration doors disclosed in thesepatents suffer from the previously described drawbacks and problemsassociated with all electrically heated refrigeration doors.

[0015] In addition to being used for conductivity, such low emissivitycoatings have been employed as another means for reducing condensationon refrigeration doors. Specifically, one method of increasing theinsulating value of glass (the “R value”), and reducing the loss of heatfrom the refrigeration compartment, is to apply a low emissivity (low E)coating to the glass. A low E coating is a microscopically thin,virtually invisible metal or metallic oxide layer(s) deposited on aglass surface to reduce the emissivity by suppressing radiativeheat-flow through the glass. Emissivity is the ratio of radiationemitted by a black body or a surface and the theoretical radiationpredicted by Planck's law. The term emissivity is used to refer toemissivity values measured in the infrared range by American Society forTesting and Materials (ASTM) standards. Emissivity is measured usingradiometric measurements and reported as hemispherical emissivity andnormal emissivity. The emissivity indicates the percentage of longinfrared wavelength radiation emitted by the coating. A lower emissivityindicates that less heat will be transmitted through the glass.Consequently, the emissivity of a sheet of glass or of an IGU impactsthe insulating value of the glass or IGU as well as the heatconductivity (the “U value”) of the glass or IGU. The U value of a sheetof glass or of an IGU is the inverse of its R value.

[0016] In a multi-pane IGU, the emissivity of the IGU, which is thecombined emissivity of the sheets of the glass that form the IGU, may beapproximated by multiplying the emissivity of all the sheets of glasstogether. For example, in a two-sheet IGU with each sheet of glasshaving an emissivity of 0.5, the total emissivity would be 0.5multiplied by 0.5 or 0.25.

[0017] While low E coatings have been applied to IGUs used inrefrigeration doors both with and without electrically heating thedoors, such coatings and IGUs are not capable of controllingcondensation and providing the required thermal insulation through thebroad range of temperatures and environments in which such refrigerationdoors are utilized without applying electricity to heat the doors. Morespecifically, notwithstanding the use of such low E coatings,refrigeration doors that are not heated have failed to providecondensation control in applications in which the interior temperatureof the refrigeration compartment is substantially near or belowfreezing.

[0018] Thus, notwithstanding the available electrically heated and lowemissivity coated refrigeration doors, there is a need for arefrigeration door: (1) that provides the necessary condensation controland thermal insulation over a broad range of temperatures andenvironments; (2) with the desired amount of visible transmittance; (3)that avoids unnecessary energy costs and undue burden on the coolingsystem by eliminating the need for supplying electrical power to heatthe door; (4) that does not require an expensive and complex electricalcontrol system, thereby minimizing design, manufacturing, operation, andmaintenance costs; and (5) that does not present a safety hazard tocustomers and a potential risk of liability and exposure tomanufacturers and retailers.

SUMMARY OF THE INVENTION

[0019] The primary objective of the present invention is to overcome thedeficiencies of the prior art described above by providing anenergy-free refrigeration door with condensation control, thermalinsulation, and a desired amount of visible transmittance.

[0020] Another key objective of the present invention is to provide arefrigeration door that does not employ electrical energy in order toreduce condensation on the glass.

[0021] Another key objective of the present invention is to provide arefrigeration door that controls condensation and that does not transfersignificant heat to the interior of the freezer or refrigerator, therebyfurther burdening the cooling system and increasing energy costs.

[0022] Still another objective of the present invention is to provide arefrigeration door with condensation control that is easier and moreeconomical to manufacture, operate, and maintain than the prior artrefrigeration doors and systems.

[0023] Yet another objective of the present invention is to provide arefrigeration door with condensation control that is easier to design,operate, and maintain.

[0024] Another objective of the present invention is to provide a methodfor making a refrigeration door with condensation control that does notuse electricity to heat the glass to control the condensation.

[0025] Yet another objective of the present invention is to provide arefrigeration door with an emissivity of less than 0.04.

[0026] Still another objective of the present invention is to provide arefrigeration door with an emissivity of approximately 0.0025.

[0027] Yet another objective of the present invention is to provide arefrigeration door with a U value of less than 0.2 BTU/hr-sq ft-F.

[0028] Still another objective of the present invention is to provide arefrigeration door with a U value of approximately 0.16 BTU/hr-sq ft-F.

[0029] The present invention achieves these objectives and others byproviding an energy-free refrigeration door, and method for making thesame, comprising a door frame housing an insulating glass unitcomprising inner, middle and outer sheets of glass. A first sealantassembly disposed around the periphery of the inner and middle sheets ofglass forms a first chamber between the inner and middle sheets ofglass. A second sealant assembly disposed around the periphery of themiddle and outer sheets of glass forms a second chamber between themiddle and outer sheets of glass. A gas, such as krypton, air, or argonis held in the first and second chambers. The outer sheet of glass andinner sheet of glass each have an unexposed surface that faces themiddle sheet of glass. A low emissivity coating is disposed on theunexposed surfaces of the inner and outer sheets of glass so that theglass door as a whole has a U value that prevents formation ofcondensation on the outer surface of the outer sheet of the glass door,without the application of electricity to heat the door, while alsoproviding the desired evaporation rate of condensation from the innerside of the inner sheet of the glass door.

[0030] Further features and advantages of the present invention, as wellas the structure and operation of various embodiments of the presentinvention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings, which are incorporated herein and formpart of the specification, illustrate various embodiments of the presentinvention and, together with the description, further serve to explainthe principles of the invention and to enable a person skilled in thepertinent art to make and use the invention. In the drawings, likereference numbers indicate identical or functionally similar elements.

[0032] A more complete appreciation of the invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

[0033]FIG. 1 depicts a refrigeration system employing the presentinvention.

[0034]FIG. 2. depicts a refrigeration door according to the presentinvention.

[0035]FIG. 3 is an illustration of a partial cross-sectional view of arefrigeration door according to the present invention.

[0036]FIG. 4 is an illustration of a partial cross-sectional view of arefrigeration door according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] In the following description, for purposes of explanation and notlimitation, specific details are set forth, such as particular coatings,coating processes, sheet thicknesses, seal assemblies, number of sheets,sheet spacings, and methods for assembling the door, etc. in order toprovide a thorough understanding of the present invention. However, itwill be apparent to one skilled in the art that the present inventionmay be practiced in other embodiments that depart from these specificdetails. Detailed descriptions of well-known coatings, coatingprocesses, sealant assemblies, and methods for assembling the door areomitted so as not to obscure the description of the present invention.For purposes of this description of the invention, terms such asexternal, internal, outer, and inner are descriptions from theperspective of the inside of the freezer or refrigerator compartment asis evident from the figures.

[0038] Testing, as well as computer modeling, has shown that a U value(the conductivity of transfer of heat through the glass) ofapproximately 0.2 BTU/hr-sq ft-F is required for the refrigeration doorto prevent condensation on the outside of the glass under theperformance requirements for the United States industry as describedabove. As discussed, however, when the door is opened, condensation mayform on the inside of the inner sheet of glass of the door because thetemperature of the inner surface of the sheet is below the dew point ofthe more humid ambient store air to which it is exposed. Thecondensation, however, will dissipate once the door is closed as themoisture evaporates into the freezer or refrigerator compartment.

[0039] While the condensation is present on the inside of the door, thecontents of the freezer or refrigerator are not visible through thedoor. Consequently, the speed of the evaporation, which determines thelength of time during which the condensation is present, is an importantdesign criterion. The more heat that is transferred through the glassdoor to the inner surface of the glass door, the faster the condensationon the inside of the door will evaporate. However, increased heattransfer through the door also results in increased energy costs fromthe cooling system. Consequently, the optimal U value of the glass doorwill be driven by numerous factors including the difference between theoutside and inside temperatures, the glass thickness, the spacing, thegas(es) used in the chamber(s) of the IGU, the number of sheets, thespacer material, the ambient humidity, the absorption coefficient of thecoating in the far infrared spectrum, as well as the desirable time forevaporation of the condensation. In addition, the costs associated withthe selected components (i.e., the gas, the sealant assembly, the glass,etc.), the energy costs, and other factors are also designconsiderations. The preferred embodiment described below provides a Uvalue of 0.16 BTU/hr-sq ft F that prevents condensation on the outsideof the door, while permitting enough heat to penetrate through the doorfrom the ambient external environment to allow condensation on theinside of the door to evaporate in a reasonable amount of time. Somerefrigeration system manufacturers require that the condensationevaporate within a few minutes and others require evaporation within oneminute. The time required for the condensation to evaporate will varyaccording to the amount of time the door is open, the humidity in thestore, the refrigeration system compartment temperature, therefrigeration system contents, the heat transferred through the door(which is dependent on the U value), and other factors.

[0040] In the preferred embodiment of the present invention, as shown inFIG. 1, a refrigeration system 5 includes a plurality of transparentrefrigeration doors 10 with each having a handle 11. As will bediscussed in more detail below, each refrigeration door 10 includes anIGU 50 mounted in a frame 55. The interior of the refrigeration systemincludes a plurality of shelves 6 for holding merchandise to be seenthrough the door. Referring to FIG. 2, the refrigeration door 10 of thepresent embodiment is mounted to the opening of the refrigeration systemwith a hinge, which allows the door to open outwards.

[0041] As discussed above, the refrigeration door 10 includes an IGU 50housed in a frame 55. As shown in FIG. 3, the IGU 50 is comprised of anouter sheet of glass 60, a middle sheet of glass 65, and an inner sheetof glass 70. The IGU 50 is housed in frame 55 and also includes a firstsealant assembly 90 that extends around the periphery of the innersurface 62 of the outer sheet 60 and the outer surface of the middlesheet 65 of glass to define a substantially hermetically sealedinsulated outer chamber 92. Similarly, a second sealant assembly 95extends around the periphery of the outer surface 72 of the inner sheet70 and inner surface of the middle sheet 65 of glass to define asubstantially hermetically sealed insulated inner chamber 94.

[0042] The outer surface 61 of the outer sheet of glass 60 is positionedadjacent the external ambient environment 7. In other words, the outersurface 61 of the outer sheet 60 is exposed to the environment in whichthe refrigerator or freezer resides. The inner surface 62 of the outersheet 60 forms part of, and is exposed to, the outer chamber 92.

[0043] In this preferred example embodiment, the outer sheet 60 is oneeighth of an inch thick, tempered, and the inner surface 62 of the outersheet 60 is coated with a low emissivity coating 63. Specifically, inthis embodiment, the low E coating is a sputter-coated low E coatingthat includes an ultra-hard titania as the base layer to ensure a highlevel of thermal performance and a high visible transmittance. Thisparticular sputter coated glass can be tempered after the coating andoffers high visible light transmission without high levels of colortinting. The outer surface 61 of outer sheet 60 is not coated. In thisembodiment, the outer sheet 60 may, for example, be a sheet of ComfortTi-PS glass, one eighth of an inch thick, manufactured by AFGIndustries, Inc. of Kingsport, Tennessee, which has a low E coatingproviding an emissivity of 0.05. As is well-known in the art, theComfort Ti-PS is cut to the appropriate size, tempered, and edged beforebeing integrated into the IGU 50.

[0044] The middle sheet of glass 65 is positioned between the outer 60and inner 70 sheets of glass and forms part of the outer chamber 92 andthe inner chamber 94. The middle sheet 65 is spaced one half inch fromthe outer sheet 60 and inner sheet 70 and is a one eighth of an inchthick, uncoated, sheet of tempered glass.

[0045] The inner sheet of glass 70 is positioned adjacent the interiorof the freezer or refrigerating compartment 9, with its inner surface 71exposed to the interior of the compartment 9. The outer surface 72 ofthe inner sheet 70 forms part of, and is exposed to, the inner chamber94. The outer surface 72 of the inner sheet 70 of glass is also coatedwith a low emissivity coating 73. In this embodiment, the coating 73 onthe outer surface 72 of the inner sheet 70 is the same as that describedabove with respect to the coating 63 of the inner surface 62 of theouter sheet 60. The inner surface 71 of inner sheet 70 is not coated. Inthis embodiment, the inner sheet 70 may also, for example, be a sheet ofComfort Ti-PS, one eighth of an inch thick, manufactured by AFGIndustries, Inc., which has the described characteristics and coating.

[0046] In this example embodiment, the chambers 92 and 94 are bothfilled with air. In alternative embodiments, each chamber may be filledwith a different gas and the chambers could be filled with krypton,argon, or other suitable gas.

[0047] The sheets 60, 65 are held apart by a first sealant assembly 90which extends around the periphery of the sheets 60, 65 maintaining theglass sheets in parallel, spaced-apart relationship creating chamber 92between the sheets 60, 65, while also sealing the chamber 92 from theexternal environment. Likewise, the sheets 65, 70 are held apart by asecond sealant assembly 95 which extends around the periphery of thesheets 65, 70 maintaining the glass sheets in parallel, spaced-apartrelationship creating chamber 94 between the sheets 65, 70, while alsosealing the chamber 94 from the external environment. The sealantassemblies 90, 95 maintain a one half inch space between the outer sheet60 and middle sheet 65 and inner sheet 70 and middle sheet 65,respectively.

[0048] The sealant assemblies 90, 95 of the present embodiment arepreferably, warm edge seals. “Warm edge” is used to describe aninsulating glass sealing assembly that reduces heat loss better thanconventional aluminum spacers and sealant combinations. Each of thesealant assemblies 90, 95 of this embodiment includes its own spacer anddesiccant, which replaces the need for a separate sealant, metallicspacer, and desiccant, and has a heat transfer rate of 0.84 Btu/hr-ft-F(sometimes referred to as a K value). The sealant assemblies 90, 95 inthis embodiment are a composite extrusion containing a combination ofpolyisobutylene sealant, hot melt butyl sealant, desiccant matrix,rubber shim and a vapor barrier. Suitable sealant assemblies of thistype are manufactured and sold by TruSeal Technologies of Beachwood,Ohio, under the name “Comfort Seal.”

[0049] Referring to FIG. 3, IGU 50 is shown. IGU 50 is comprised ofglass sheets 60, 65, and 70 integrated by sealant assemblies 90 and 95.IGU 50 is installed in frame 55 in any suitable manner well-known tothose skilled in the art. The frame 55 is made from extruded plastic orother suitable well-known frame materials, such as extruded aluminum,fiber glass or other material. If, in an alternative embodiment theframe 55 is formed of aluminum or other material, the door may requireheating along its edges to ensure condensation control around the edgesof the door.

[0050] Referring to FIG. 1, a refrigeration system 5 is shown. The doorframe 55 is coupled to the refrigeration compartment 8 in any suitablefashion as is well known in the art, such as a single door long hinge,multiple hinges, or in a slot for sliding the door open and closed. Inaddition, the frame may include a door handle 11 or other suitableactuating means as is appropriate for the application. The refrigerationsystem 5, of which the door 10 forms a part, may be any system used forcooling a compartment, such as that disclosed in U.S. Pat. No.6,148,563, which is hereby incorporated herein by reference.

[0051] The above preferred embodiment provides a refrigeration door witha U value of 0.16 BTU/hr-sq ft-F (and emissivity of 0.0025), which hasbeen found to be suitable for freezer door applications requiring theperformance standards identified above with respect to the United Statesindustry. A U value of 0.16 BTU/hr-sq ft-F permits the refrigerationdoor to easily meet the required performance standards, while alsoallowing enough heat to penetrate through the door from the externalambient environment to evaporate condensation formed on the inside ofthe door in a reasonable time period. In addition, the preferredembodiment provides a visible light transmittance of sixty-six percent(66%).

[0052] As an alternative to the Comfort Ti-PS glass, other low E coatedglass may be used, such as, for example, Comfort Ti-R, Comfort Ti-AC,Comfort Ti-RTC, and Comfort Ti-ACTC, all of which are available from AFGIndustries, Inc., which like Comfort Ti-PS, are titania/silver based lowE coated glass manufactured by AFG Industries, Inc. Another suitabletype of glass is Comfort E2, which is coated with a pyrolytic processand is a fluorine doped tin oxide low E coated glass, one eighth of aninch thick, and which is manufactured by AFG Industries, Inc. Comfort E2is suitable for some of the less stringent performance standards becauseof its higher emissivity.

[0053] The U value of the refrigeration door 10 is determined by anumber of design factors including the number of sheets of glass, thethickness of the sheets, the emissivity of the IGU, the spacing betweenthe sheets, and the gas in the chamber(s). In the three panerefrigeration door 10 of the preferred embodiment described above, the Uvalue of 0.16 BTU/hr-sq ft-F is accomplished using air as the gas beingheld in the chambers, glass thicknesses of one eighth of an inch on allsheets, one half inch spacing, and an IGU emissivity of 0.0025. However,each of these factors can be varied resulting in numerous permutationsof values that could be combined to provide the same U value. Inaddition, other applications may require a smaller or larger U valuedepending on the environment, costs constraints, and other requirementsor considerations.

[0054] A number of computer simulations have been performed to determinethe U values of numerous IGUs for use in refrigeration doors 10 with arange of values of each of the various design parameters combined indifferent permutations. The table below includes the design parametersand corresponding calculated U values for a number of three pane IGUconfigurations. In addition to the design parameters listed in Table 1below, all of the three pane IGU U value calculations were computed witheach pane being one eighth of an inch thick, and a total of two sides ofthe three panes being low E coated. Tempering of the glass does notsignificantly effect the calculated performance values. TABLE 1 Spacingbetween Sheets Gas in Type of Emissivity of U value (inches) ChambersCoating IGU (Btu/hr-sq ft-F) ½ air Ti-PS 0.0025 0.16 {fraction (5/16)}air Ti-PS 0.0025 0.22 ½ argon Ti-PS 0.0025 0.12 {fraction (5/16)} argonTi-PS 0.0025 0.17 ½ krypton Ti-PS 0.0025 0.11 {fraction (5/16)} kryptonTi-PS 0.0025 0.11 ½ air CE2 0.04 0.20 {fraction (5/16)} air CE2 0.040.26 ½ argon CE2 0.04 0.17 {fraction (5/16)} argon CE2 0.04 0.21 ½krypton CE2 0.04 0.15 {fraction (5/16)} krypton CE2 0.04 0.15

[0055] In each of the tables included herein, “Ti-PS” refers to the lowE coating of AFG Industries' Comfort Ti-PS glass and “CE2” refers to thelow E coating of AFG Industries' Comfort E2 glass, both described above.In addition, the U values in the tables are calculated as “center of theglass” values, because the computer simulation does not have thecapability to consider the sealant assembly. Consequently, there are nosealant assembly data or design criteria listed in the tables.

[0056] In an alternative two pane embodiment of the present inventionshown in FIG. 4, the IGU 50 includes an outer sheet 60 and inner sheet70 of glass, the frame 55, and a sealant assembly 90. In this two-paneembodiment, both the outer sheet 60 and inner sheet 70 are one eighth ofan inch thick and include the same low E coating as described in thefirst embodiment, which is titania based silver low E coating. Again,both the outer sheet 60 and inner sheet 70 may, for example, be a sheetof Comfort Ti-PS glass, one eighth of an inch thick, manufactured by AFGIndustries, Inc. The coated sides of the sheets 60 and 70 are on theunexposed surfaces of the sheets, sides 62 and 72, respectively, whichform part of the chamber 92. In addition, the same sealant assembly 90described above (the Comfort Seal) may be used and acts to provide aspacing of one half inch between the outer 60 and inner 70 sheets ofglass.

[0057] Table 2 below includes design parameters and the correspondingcalculated U values for a number of two pane IGUs. In addition to thedesign parameters listed in the table below, all of the two panecalculations were computed with each pane being one eighth of an inchthick, and a total of two sides of the two panes being low E coated.Tempering of the glass does not significantly effect the calculatedperformance values. TABLE 2 Spacing between Sheets Gas in Type ofEmissivity of U value (inches) Chambers Coating IGU (Btu/hr-sq ft-F) ½air Ti-PS 0.0025 0.29 {fraction (5/16)} air Ti-PS 0.0025 0.36 ½ argonTi-PS 0.0025 0.23 {fraction (5/16)} argon Ti-PS 0.0025 0.28 ½ kryptonTi-PS 0.0025 0.22 {fraction (5/16)} krypton Ti-PS 0.0025 0.20 ½ air CE20.04 0.32 {fraction (5/16)} air CE2 0.04 0.39 ½ argon CE2 0.04 0.27{fraction (5/16)} argon CE2 0.04 0.31 ½ krypton CE2 0.04 0.26 {fraction(5/16)} krypton CE2 0.04 0.24

[0058] In alternative embodiments, any suitable type of coatingprocesses may be employed including pyrolytic (e.g., as in the ComfortE2), which is often referred to as chemical vapor deposition (CVD),spray, and sputter coating (e.g., as in the Comfort Ti-PS). Furthermore,these processes may be applied using well-known off-line or on-linemanufacturing methods as is suitable and appropriate for the quantityand type of production and process. Likewise, any suitable low E coatingmay be employed including silver based, titania based, or fluorine dopedtin oxide coating.

[0059] Although the embodiments described above include low E coatingson the unexposed surfaces of two sheets of glass, other embodiments ofthe present invention might include a low E coating applied to only onesheet of glass on either side, or on both sides. Likewise, in otherembodiments the middle sheet of glass (of a three pane embodiment) mayinclude a low E coating on either side (or both sides) instead of, or inaddition to, coatings on the inner sheet 70 and outer sheet 60 of glass.

[0060] In yet another three pane embodiment, the inner sheet of glass 70does not have a low E coating on either side of the sheet of glass 70.Likewise, in an alternative to the two sheet embodiment described above,the low E coating is present on only one sheet, or on both sides of bothsheets. In general, the number of sheets that have the low E coating andthe side (or sides) that have the coating is a design choice. The totalemissivity of the IGU, which along with other factors determines the Ufactor of the door, is more important with respect to the thermalperformance than which side or sides of which sheet(s) are coated. Inaddition, although the embodiments described herein have emissivities ofless than or equal to 0.04 for refrigeration door applications, using ahigh performance gas (such as krypton) may enable an IGU with anemissivity of slightly more than 0.04 to provide the necessarycondensation control in some circumstances.

[0061] In other embodiments, other sealant assemblies may be employedincluding for example, an all-foam, non-metal assembly such as the SuperSpacer, manufactured by EdgeTech, Inc, which has a heat transfer rate ofapproximately 1.51 Btu/hr-ft-F. Another suitable sealant assembly is theThermoPlastic Spacersystem (TPS) manufactured by Lenhardt MaschinenbauGmbH, which has a heat transfer rate of approximately 1.73 Btu/hr-ft-F.

[0062] The spacing in the above disclosed embodiments is one half inch.However, while the preferred spacing ranges between five sixteenths ofan inch to one half inch, other embodiments of the invention may usespacings up to three quarters of an inch. In addition, while the abovedisclosed embodiments employ glass one eighth of an inch thick that istempered (except for the middle sheet), other embodiments may useuntempered glass or thicknesses that are greater than, or less than, oneeighth of an inch.

[0063] The design parameters of an embodiment of the present inventionwill be determined, in part, by the application or intended use of theembodiment. More specifically, the exterior ambient temperature,interior temperature, and exterior ambient humidity (and associated dewpoint) are important factors in determining the necessary U value forthe design, which in turn, determines the design parameters (type ofglass, emissivity, number of sheets, gas, etc.).

[0064] The left five columns of Table 3 below provide a list ofcalculated U values for various applications of the intended use andincludes the exterior temperature, interior temperature, exteriorhumidity, and calculated dew point for each U value. In addition, theright three columns of Table 3 provide an embodiment of the inventionthat will provide the necessary U value. TABLE 3 Calculated U Values forVarious Environmental Parameters IGU Design Variables Dewpoint Maximumfor Satisfying Identified Exterior Interior U Value (Outside Relative UValue Temp Temp Btu/ Glass T) Humidity Glass Spacing Gas In Deg F. DegF. hr-sq ft-F Deg F. Percent (Two Sheets) Inches Chambers 80 −40 0.1964.9 60.1 Ti-PS ⅜ air 72 0 0.27 57.4 60   CE2 {fraction (5/16)} air 80−40 0.15 67.6 66.0 CE2 ⅜ krypton 80 −40 0.18 65.7 61.8 CE2 ⅜ argon 80−40 0.25 60.3 51.1 CE2 ⅜ air 80 −40 0.16 67.3 65.3 CE2 ½ krypton 80 −400.17 66.5 63.5 CE2 ½ argon 80 −40 0.20 64.1 58.5 CE2 ½ air 80 −40 0.1170.6 73.1 Ti-PS ⅜ krypton 80 −40 0.14 68.6 68.3 Ti-PS ⅜ argon 80 −400.19 65.0 60.3 Ti-PS ⅜ air 80 −40 0.12 70.2 72.1 Ti-PS ½ krypton 80 −400.13 69.4 70.2 Ti-PS ½ argon 80 −40 0.17 66.7 64.0 Ti-PS ½ air 72 −100.18 61.2 68.9 CE2 ⅜ argon 72 0 0.18 62.1 71.1 CE2 ⅜ argon 72 10 0.1863.0 73.4 CE2 ⅜ argon 70 0 0.18 60.3 71.4 CE2 ⅜ argon 80 0 0.18 69.269.7 CE2 ⅜ argon 90 0 0.18 78.1 68.3 CE2 ⅜ argon 70 −20 0.21 55.5 60.1CE2 ⅜ air 86 −22 0.11 77.5 75.9 Ti-PS ⅜ krypton 80 −40 0.19 65.0 60.3CE1 ½ air 70 32 0.18 63.4 79.6 CE2 ⅜ argon 80 32 0.18 72.2 77.2 CE2 ⅜argon 90 32 0.18 81.0 75.0 CE2 ⅜ argon

[0065] The design parameters of Table 3 identify the type of glass(which is one eighth of an inch thick), the spacing between sheets, andthe gas in the chambers. In addition, all of the IGUs of the Table 3include a third, non-coated sheet of glass that is one eighth of an inchthick, and that is disposed between the two sheets of glass identifiedin the table. CE1 in the Table 3 refers to Comfort El, which has anemissivity of 0.35 and is sold by AFG Industries, Inc.

[0066] The foregoing has described the principles, embodiments, andmodes of operation of the present invention. However, the inventionshould not be construed as being limited to the particular embodimentsdescribed above, as they should be regarded as being illustrative andnot as restrictive. It should be appreciated that variations may be madein those embodiments by those skilled in the art without departing fromthe scope of the present invention.

[0067] While the application of the present invention has been describedin the application of a refrigerator or freezer door, other applicationsmight include vending machines, skylights, or refrigerated trucks. Insome of these applications, condensation on the second or colder side ofthe glass may not be an issue because the glass is not in a door that isperiodically opened exposing the cold glass to a more humid environment.As a result, the key factors in designing the glass are economics (i.e.,the energy costs and the cost of the glass and its installation),visible transmittance, durability, and other considerations.

[0068] While a preferred embodiment of the present invention has beendescribed above, it should be understood that it has been presented byway of example only, and not limitation. Thus, the breadth and scope ofthe present invention should not be limited by the above describedexemplary embodiment.

[0069] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A refrigeration door adapted to be mounted on arefrigerating compartment, said door comprising: an inner sheet of glassincluding a first surface and a second surface, said first surface ofsaid inner sheet being disposed adjacent the interior of therefrigerating compartment; an outer sheet of glass including a firstsurface and a second surface, said first surface of said outer sheetbeing disposed adjacent the exterior environment of the refrigeratingcompartment; a middle sheet of glass disposed between said inner andouter sheets of glass; a first sealant assembly disposed around theperiphery of said inner sheet of glass and said middle sheet of glassfor maintaining said inner sheet and said middle sheet in spaced-apartrelationship from each other; a second sealant assembly disposed aroundthe periphery of said middle sheet of glass and said outer sheet ofglass for maintaining said middle sheet and said outer sheet inspaced-apart relationship from each other; a first low emissivitycoating adjacent the second surface of said inner sheet of glass; asecond low emissivity coating adjacent the second surface of said outersheet of glass; said inner sheet, outer sheet, middle sheet, firstsealant assembly, second sealant assembly, and said first and second lowemissivity coatings forming an insulating glass unit having a U valuesubstantially equal to or less than 0.2 BTU/hr-sq ft-F substantiallypreventing the formation of condensation on said first surface of saidouter sheet of glass without the application of electricity for heatingsaid first surface of said outer sheet of glass; and a frame securedaround the periphery of said insulating glass unit.
 2. The refrigerationdoor of claim 1, further comprising: a first chamber defined by saidinner sheet of glass, said middle sheet of glass, and said first sealantassembly; a second chamber defined by said middle sheet of glass, saidouter sheet of glass, and said second sealant assembly; and a gasdisposed in said first and second chambers.
 3. The refrigeration door ofclaim 2, wherein: said inner, said middle, and said outer sheets ofglass have a thickness substantially equal to one eighth of an inch;said inner and said middle sheets of glass being spaced apart a distancesubstantially equal to one half inch; and said middle and said outersheets of glass being spaced apart a distance substantially equal to onehalf inch.
 4. The refrigeration door of claim 2, wherein at least onesheet of glass is formed of Comfort Ti-PS.
 5. The refrigeration door ofclaim 2, wherein said first sealant assembly and said second sealantassembly each have a heat transfer rate substantially equal to or lessthan 1.73 Btu/hr-ft-F.
 6. The refrigeration door of claim 5, wherein:said inner, said middle and said outer sheets of glass having athickness substantially equal to one eighth of an inch; said inner andsaid middle sheets of glass being spaced apart a distance substantiallyequal to one half inch; and said middle and said outer sheets of glassbeing spaced apart a distance substantially equal to one half inch. 7.The refrigeration door of claim 2, wherein said gas in said firstchamber and said second chamber are the same.
 8. The refrigeration doorof claim 2, wherein said gas in said first chamber and said secondchamber are not the same.
 9. The refrigeration door of claim 2, whereinsaid gas is selected from the group consisting of argon, krypton, andair.
 10. The refrigeration door of claim 1, wherein said insulatingglass unit has a U value substantially equal to or less than 0.16BTU/hr-sq ft-F.
 11. The refrigeration door of claim 1, wherein saidouter sheet and said inner sheet each have an emissivity substantiallyequal to or less than 0.05.
 12. The refrigeration door of claim 1,wherein said outer sheet and said inner sheet each have an emissivitysubstantially equal to or less than 0.03.
 13. The refrigeration door ofclaim 1, wherein said insulating glass unit has an emissivitysubstantially equal to or less than 0.04.
 14. The refrigeration door ofclaim 1, wherein said insulating glass unit has an emissivitysubstantially equal to or less than 0.01.
 15. The refrigeration door ofclaim 1, wherein said insulating glass unit has an emissivitysubstantially equal to or less than 0.0025.
 16. The refrigeration doorof claim 2, wherein said first and second low emissivity coatings areselected from the group consisting of a titania based silver andfluorine doped tin oxide.
 17. The refrigeration door of claim 2, whereinsaid first and second low emissivity coatings are applied with a processselected from the group consisting of sputter coating, pyrolytic coatingand spray coating.
 18. The refrigeration door of claim 2, wherein saidframe is formed from a material selected from the group consisting ofextruded plastic, aluminum, and fiber glass.
 19. The refrigeration doorof claim 1, wherein the interior temperature of the refrigeratingcompartment is substantially equal to or less than minus twenty degreesFahrenheit; the temperature of the exterior environment is substantiallyequal to or greater than seventy degrees Fahrenheit; and the humidity inthe exterior environment is substantially equal to or greater than sixtypercent; and wherein said first surface of said outer sheet of glass issubstantially free of condensation.
 20. The refrigeration door of claim1, wherein the interior temperature of the refrigerating compartment issubstantially equal to or less than minus forty degrees Fahrenheit; thetemperature of the exterior environment is substantially equal to orgreater than eighty degrees Fahrenheit; and the humidity in the exteriorenvironment is substantially equal to or greater than sixty percent; andwherein said first surface of said outer sheet of glass is substantiallyfree of condensation.
 21. The refrigeration door of claim 1, wherein theinterior temperature of the refrigerating compartment is substantiallyequal to or less than zero degrees Fahrenheit; the temperature of theexterior environment is substantially equal to or greater than seventytwo degrees Fahrenheit; and the humidity in the ambient environment issubstantially equal to or greater than sixty percent; and wherein saidfirst surface of said outer sheet of glass is substantially free ofcondensation.
 22. The refrigeration door of claim 2, wherein at leastone sheet of glass is formed of Comfort E2.
 23. The refrigeration doorof claim 1, wherein said first sealant assembly and said second sealantassembly each have a heat transfer rate substantially equal to or lessthan 1.73 Btu/hr-ft-F.
 24. The refrigeration door of claim 1, whereinsaid first sealant assembly and said second sealant assembly each have aheat transfer rate substantially equal to or less than 1.51 Btu/hr-ft-F.25. The refrigeration door of claim 1, wherein said first sealantassembly and said second sealant assembly each have a heat transfer ratesubstantially equal to or less than 0.84 Btu/hr-ft-F.
 26. Arefrigeration door adapted to be mounted on a refrigerating compartment,said door comprising: an inner sheet of glass including a first surfaceand a second surface, said first surface of said inner sheet beingdisposed adjacent the interior of the refrigerating compartment; anouter sheet of glass including a first surface and a second surface,said first surface of said outer sheet being disposed adjacent theexterior environment of the refrigerating compartment; a middle sheet ofglass disposed between said inner and outer sheets of glass; a firstsealant assembly disposed around the periphery of said inner sheet ofglass and said middle sheet of glass for maintaining said inner sheetand said middle sheet in spaced-apart relationship from each other; asecond sealant assembly disposed around the periphery of said middlesheet of glass and said outer sheet of glass for maintaining said middlesheet and said outer sheet in spaced-apart relationship from each other;a first low emissivity coating adjacent the second surface of said innersheet of glass; a second low emissivity coating adjacent the secondsurface of said outer sheet of glass; said inner sheet, outer sheet,middle sheet, first sealant assembly, second sealant assembly, and saidfirst and second low emissivity coatings forming an insulating glassunit having an emissivity substantially equal to or less than 0.04substantially preventing the formation of condensation on said firstsurface of said outer sheet of glass without the application ofelectricity for heating said first surface of said outer sheet of glass;and a frame secured around the periphery of said insulating glass unit.27. The refrigeration door of claim 26, further comprising: a firstchamber defined by said inner sheet of glass, said middle sheet ofglass, and said first sealant assembly; a second chamber defined by saidmiddle sheet of glass, said outer sheet of glass, and said secondsealant assembly; and a gas disposed in said first and second chambers.28. The refrigeration door of claim 27, wherein: said inner, saidmiddle, and said outer sheets of glass have a thickness substantiallyequal to one eighth of an inch; said inner and said middle sheets ofglass being spaced apart a distance substantially equal to one halfinch; and said middle and said outer sheets of glass being spaced aparta distance substantially equal to one half inch.
 29. The refrigerationdoor of claim 27, wherein at least one sheet of glass is formed ofComfort Ti-PS.
 30. The refrigeration door of claim 27, wherein said gasis selected from the group consisting of argon, krypton, and air. 31.The refrigeration door of claim 26, wherein said insulating glass unithas a U value substantially equal to or less than 0.16 BTU/hr-sq ft-F.32. The refrigeration door of claim 26, wherein said outer sheet andsaid inner sheet each have an emissivity substantially equal to or lessthan 0.05.
 33. The refrigeration door of claim 26, wherein said outersheet and said inner sheet each have an emissivity substantially equalto or less than 0.03.
 34. The refrigeration door of claim 26, whereinsaid insulating glass unit has a U value substantially equal to or lessthan 0.2 BTU/hr-sq ft-F.
 35. The refrigeration door of claim 26, whereinsaid insulating glass unit has an emissivity substantially equal to orless than 0.01.
 36. The refrigeration door of claim 26, wherein saidinsulating glass unit has an emissivity substantially equal to or lessthan 0.0025.
 37. The refrigeration door of claim 27, wherein said lowemissivity coatings are selected from the group consisting of a titaniabased silver and fluorine doped tin oxide.
 38. The refrigeration door ofclaim 27, wherein said low emissivity coatings are applied with aprocess selected from the group consisting of sputter coating, pyrolyticcoating and spray coating.
 39. The refrigeration door of claim 27,wherein said frame is formed from a material selected from the groupconsisting of extruded plastic, aluminum, and fiber glass.
 40. Therefrigeration door of claim 26, wherein the interior temperature of therefrigerating compartment is substantially equal to or less than minustwenty degrees Fahrenheit; the temperature of the exterior environmentis substantially equal to or greater than seventy degrees Fahrenheit;and the humidity in the exterior environment is substantially equal toor greater than sixty percent; and wherein said first surface of saidouter sheet of glass is substantially free of condensation.
 41. Therefrigeration door of claim 26, wherein the interior temperature of therefrigerating compartment is substantially equal to or less than minusforty degrees Fahrenheit; the temperature of the exterior environment issubstantially equal to or greater than eighty degrees Fahrenheit; andthe humidity in the exterior environment is substantially equal to orgreater than sixty percent; and wherein said first surface of said outersheet of glass is substantially free of condensation.
 42. Therefrigeration door of claim 26, wherein the interior temperature of therefrigerating compartment is substantially equal to or less than minuszero degrees Fahrenheit; the temperature of the exterior environment issubstantially equal to or greater than seventy-two degrees Fahrenheit;and the humidity in the ambient environment is substantially equal to orgreater than sixty percent; and wherein said first surface of said outersheet of glass is substantially free of condensation.
 43. Therefrigeration door of claim 27, wherein at least one sheet of glass isformed of Comfort E2.
 44. The refrigeration door of claim 26, whereinsaid first sealant assembly and said second sealant assembly each have aheat transfer rate substantially equal to or less than 1.73 Btu/hr-ft-F.45. The refrigeration door of claim 26, wherein first sealant assemblyand said second sealant assembly each have a heat transfer ratesubstantially equal to or less than 1.51 Btu/hr-ft-F.
 46. Therefrigeration door of claim 26, wherein first sealant assembly and saidsecond sealant assembly each have a heat transfer rate substantiallyequal to or less than 0.84 Btu/hr-ft-F.
 47. A refrigeration door havingan outer surface and adapted to be mounted on a refrigeratingcompartment, said door comprising: a first sheet of glass; a secondsheet of glass; a first sealant assembly disposed around the peripheryof said first sheet of glass and said second sheet of glass formaintaining said first sheet and said second sheet in spaced-apartrelationship from each other; a first low emissivity coating adjacent asurface of said first sheet or said second sheet of glass; said firstsheet and second sheets of glass, said first sealant assembly, and saidfirst low emissivity coating forming an insulating glass unit having a Uvalue substantially equal to or less than 0.2 BTU/hr-sq ft-F; and aframe secured around the periphery of said insulating glass unit. 48.The refrigerator door of claim 47, further comprising: a third sheet ofglass; a second sealant assembly disposed around the periphery of saidsecond sheet of glass and said third sheet of glass for maintaining saidsecond sheet and said third sheet in spaced-apart relationship from eachother; and wherein said insulating glass unit further includes saidthird sheet of glass and said second sealant assembly.
 49. Therefrigeration door of claim 48, further including a second lowemissivity coating adjacent a surface of said first sheet, said secondsheet, or said third sheet of glass.
 50. The refrigeration door of claim49, wherein the U value of said insulating glass unit is effective tosubstantially prevent the formation of condensation on the outer surfaceof the door without the application of electricity for heating the outersurface when the interior temperature of the refrigerating compartmentis substantially equal to or less than zero degrees Fahrenheit; thetemperature of the exterior environment is substantially equal to orgreater than seventy-two degrees Fahrenheit; and the humidity in theambient environment is substantially equal to or greater than sixtypercent.
 51. The refrigerator door of claim 47, wherein the U value ofsaid insulating glass unit is effective to substantially prevent theformation of condensation on the outer surface of the door without theapplication of electricity for heating the outer surface when theinterior temperature of the refrigerating compartment is substantiallyequal to or less than minus zero degrees Fahrenheit; the temperature ofthe exterior environment is substantially equal to or greater thanseventy-two degrees Fahrenheit; and the humidity in the ambientenvironment is substantially equal to or greater than sixty percent. 52.The refrigeration door of claim 51, further comprising: a first chamberdefined by said first sheet of glass, said second sheet of glass, andsaid first sealant assembly; and a gas disposed in said first chamber.53. The refrigeration door of claim 52, wherein said first sealantassembly has a heat transfer rate substantially equal to or less than1.73 Btu/hr-ft-F.
 54. The refrigeration door of claim 43, wherein saidgas is selected from the group consisting of argon, krypton, and air.55. The refrigeration door of claim 47, wherein said insulating glassunit has a U value substantially equal to or less than 0.16 BTU/hr-sqft-F.
 56. The refrigeration door of claim 47, wherein said insulatingglass unit has an emissivity substantially equal to or less than 0.04.57. The refrigeration door of claim 47, wherein said insulating glassunit has an emissivity substantially equal to or less than 0.01.
 58. Therefrigeration door of claim 47, wherein insulating glass unit has anemissivity substantially equal to or less than 0.0025.
 59. Therefrigeration door of claim 47, wherein the interior temperature of therefrigerating compartment is substantially equal to or less than minustwenty degrees Fahrenheit; the temperature of the exterior environmentis substantially equal to or greater than seventy degrees Fahrenheit;and the humidity in the exterior environment is substantially equal toor greater than sixty percent; and wherein the outer surface of the dooris substantially free of condensation.
 60. The refrigeration door ofclaim 47, wherein the interior temperature of the refrigeratingcompartment is substantially equal to or less than minus forty degreesFahrenheit; the temperature of the exterior environment is substantiallyequal to or greater than eighty degrees Fahrenheit; and the humidity inthe exterior environment is substantially equal to or greater than sixtypercent; and wherein the outer surface of the door is substantially freeof condensation.
 61. A refrigeration door having an outside surface andadapted to be mounted on a refrigerating compartment, said doorcomprising: a first sheet of glass; a second sheet of glass; a firstsealant assembly disposed around the periphery of said first sheet ofglass and said second sheet of glass for maintaining said first sheetand said second sheet in spaced-apart relationship from each other; afirst low emissivity coating adjacent a surface of said first sheet orsaid second sheet of glass; said first sheet and second sheets of glass,said first sealant assembly, and said first low emissivity coatingforming an insulating glass unit having an emissivity substantiallyequal to or less than 0.04 substantially preventing the formation ofcondensation on the outside surface of the refrigeration door withoutthe application of electricity for heating said outer surface; and aframe secured around the periphery of said insulating glass unit. 62.The refrigerator door of claim 61, further comprising: a third sheet ofglass; a second sealant assembly disposed around the periphery of saidsecond sheet of glass and said third sheet of glass for maintaining saidsecond sheet and said third sheet in spaced-apart relationship from eachother; and wherein said insulating glass unit further includes saidthird sheet of glass and said second sealant assembly.
 63. Therefrigeration door of claim 62, further including a second lowemissivity coating adjacent a surface of said first sheet, said secondsheet, or said third sheet of glass.
 64. The refrigeration door of claim61, further comprising: a first chamber defined by said first sheet ofglass, said second sheet of glass, and said first sealant assembly; anda gas disposed in said first chamber.
 65. The refrigeration door ofclaim 64, wherein said first sealant assembly has a heat transfer ratesubstantially equal to or less than 1.73 Btu/hr-ft-F.
 66. Therefrigeration door of claim 65, wherein said gas is selected from thegroup consisting of argon, krypton, and air.
 67. The refrigeration doorof claim 61, wherein said insulating glass unit has a U valuesubstantially equal to or less than 0.16 BTU/hr-sq ft-F.
 68. Therefrigeration door of claim 61, wherein said insulating glass unit has aU value substantially equal to or less than 0.20 BTU/hr-sq ft-F.
 69. Therefrigeration door of claim 61, wherein said insulating glass unit hasan emissivity substantially equal to or less than 0.01.
 70. Therefrigeration door of claim 61, wherein insulating glass unit has anemissivity substantially equal to or less than 0.0025.
 71. A method ofmanufacturing a refrigeration door component having an outer surface,said method comprising the steps of: providing a first sheet of glassproviding a second sheet of glass; providing a first low emissivitycoating adjacent a surface of said first sheet of glass or said secondsheet of glass; disposing a first sealant assembly around the peripheryof said first sheet of glass and said second sheet of glass to maintainsaid first sheet and said second sheet in spaced-apart relationship fromeach other; and said first sheet of glass, said second sheet of glass,and said first sealant assembly forming an insulating glass unit havinga U value substantially equal to or less than 0.2 BTU/hr-sq ft-Fsubstantially preventing the formation of condensation on the outersurface of the refrigeration door component without the application ofelectricity for heating the door component.
 72. The method of claim 71,wherein said first sheet of glass, said second sheet of glass, and saidfirst sealant assembly define a first chamber; and further comprisingthe step of disposing a gas in said first chamber.
 73. The method ofclaim 71, further comprising the steps of: providing a third sheet ofglass; disposing a second sealant assembly disposed around the peripheryof said second sheet of glass and said third of glass for maintainingsaid second sheet and said third sheet in spaced-apart relationship fromeach other; and wherein said insulating glass unit further includes saidthird sheet of glass and said second sealant assembly.
 74. The method ofclaim 73, wherein said third sheet of glass includes a low emissivitycoating adjacent a surface of said third sheet of glass.
 75. The methodof claim 71, wherein said first sheet of glass is formed of ComfortTi-PS.
 76. The method of claim 71, wherein said first sealant assemblyhas a heat transfer rate substantially equal to or less than 1.73Btu/hr-ft-F.
 77. The method of claim 76, wherein: said first and saidsecond sheets of glass having a thickness substantially equal to oneeighth of an inch; and said first and said second sheets of glass beingspaced apart a distance substantially equal to one half inch.
 78. Themethod of claim 71, further including the step of disposing saidinsulating glass unit in a door frame.
 79. The method of claim 72,wherein said gas is selected from the group consisting of argon,krypton, and air.
 80. The method of claim 71, wherein said insulatingglass unit has a U value substantially equal to or less than 0.16BTU/hr-sq ft-F.
 81. The method of claim 71, wherein said insulatingglass unit has an emissivity substantially equal to or less than 0.04.82. The method of claim 71, wherein said insulating glass unit has anemissivity substantially equal to or less than 0.01.
 83. The method ofclaim 71, wherein said insulating glass unit has an emissivitysubstantially equal to or less than 0.0025.
 84. The method of claim 71,wherein said low emissivity coating is selected from the groupconsisting of a titania based silver and fluorine doped tin oxide. 85.The method of claim 71, wherein said low emissivity coating is appliedwith a process selected from the group consisting of sputter coating,pyrolytic coating and spray coating.
 86. The method of claim 72, whereinsaid first sheet of glass is formed of Comfort E2.
 87. The refrigerationdoor of claim 73, wherein said first and second sealant assemblies havea heat transfer rate substantially equal to or less than 1.73Btu/hr-ft-F.
 88. The refrigeration door of claim 71, wherein said firstsealant assembly has a heat transfer rate substantially equal to or lessthan 1.51 Btu/hr-ft-F.
 89. The refrigeration door of claim 71, whereinsaid first sealant assembly has a heat transfer rate substantially equalto or less than 0.84 Btu/hr-ft-F.
 90. A method of manufacturing arefrigeration door component having an outer surface, said methodcomprising the steps of: providing a first sheet of glass; providing asecond sheet of glass; providing a first low emissivity coating adjacenta surface of said first sheet of glass or said second sheet of glass;disposing a first sealant assembly around the periphery of said firstsheet of glass and said second sheet of glass to maintain said firstsheet and said second sheet in spaced-apart relationship from eachother; and said first sheet of glass, said second sheet of glass, andsaid first sealant assembly forming an insulating glass unit having anemissivity substantially equal to or less than 0.04 substantiallypreventing the formation of condensation on the outer surface of therefrigeration door component without the application of electricity forheating the door component.
 91. The method of claim 90, wherein saidfirst sheet of glass, said second sheet of glass, and said first sealantassembly define a first chamber; and further comprising the step ofdisposing a gas in said first chamber.
 92. The method of claim 90,further comprising the steps of: providing a third sheet of glass;disposing a second sealant assembly disposed around the periphery ofsaid second sheet of glass and said third of glass for maintaining saidsecond sheet and said third sheet in spaced-apart relationship from eachother; and wherein said insulating glass unit further includes saidthird sheet of glass and said second sealant assembly.
 93. The method ofclaim 92, wherein said third sheet of glass includes a low emissivitycoating adjacent a surface of said third sheet of glass.
 94. The methodof claim 90, wherein said first sealant assembly has a heat transferrate substantially equal to or less than 1.73 Btu/hr-ft-F.
 95. Themethod of claim 90, further including the step of disposing saidinsulating glass unit in a door frame.
 96. The method of claim 91,further including the step of disposing said insulating glass unit in adoor frame.
 97. The method of claim 96, wherein said gas is selectedfrom the group consisting of argon, krypton, and air.
 98. The method ofclaim 90, wherein said insulating glass unit has a U value substantiallyequal to or less than 0.2 BTU/hr-sq ft-F.
 99. The method of claim 90,wherein said insulating glass unit has an emissivity substantially equalto or less than 0.01.
 100. The method of claim 90, wherein saidinsulating glass unit has an emissivity substantially equal to or lessthan 0.0025.
 101. The refrigeration door of claim 92, wherein said firstand second sealant assemblies have a heat transfer rate substantiallyequal to or less than 1.73 Btu/hr-ft-F.
 102. The refrigeration door ofclaim 90, wherein said first sealant assembly has a heat transfer ratesubstantially equal to or less than 1.51 Btu/hr-ft-F.
 103. Therefrigeration door of claim 90, wherein said first sealant assembly hasa heat transfer rate substantially equal to or less than 0.84Btu/hr-ft-F.
 104. A substantially transparent insulating glass unithaving an outer surface and being for use with a refrigeratingcompartment residing in an exterior environment and having an interiorrefrigerating compartment; said insulating glass unit door comprising: afirst sheet of glass; a second sheet of glass; a first sealant assemblydisposed around the periphery of said first sheet of glass and saidsecond sheet of glass for maintaining said first sheet and said secondsheet in spaced-apart relationship from each other; a first lowemissivity coating adjacent a surface of said first sheet or said secondsheet of glass, and said first sheet of glass, said second sheet ofglass, and said first sealant assembly providing the insulating glassunit with a U value effective to substantially prevent the formationcondensation on the outer surface without the application of aelectricity to heat the outer surface of the insulating glass unit whenthe interior temperature of the refrigerating compartment issubstantially equal to or less than zero degrees Fahrenheit; thetemperature of the exterior environment is substantially equal to orgreater than seventy degrees Fahrenheit; and the humidity in theexterior environment is substantially equal to or greater than sixtypercent.
 105. The door of claim 104, further comprising: a third sheetof glass; and a second sealant assembly disposed around the periphery ofsaid second sheet of glass and said third of glass for maintaining saidfirst sheet and said second sheet in spaced-apart relationship from eachother.
 106. The door of claim 105, further including a second lowemissivity coating adjacent a surface of said first sheet, said secondsheet or said third sheet of glass.
 107. The door of claim 106 whereinthe insulating glass unit has a U value that substantially prevents theformation condensation on the outer surface when the interiortemperature of the refrigerating compartment is substantially equal toor less than minus forty degrees Fahrenheit; the temperature of theexterior environment is at substantially equal to or greater than eightydegrees Fahrenheit; and the humidity in the exterior environment issubstantially equal to or greater than sixty percent.
 108. The door ofclaim 106, wherein said low emissivity coating is effective to cause theinsulating glass unit to have a U value substantially equal to or lessthan 0.2 BTU/hr-sq ft-F.
 109. The refrigeration door of claim 105,wherein said first sealant assembly and said second sealant assemblyeach have a heat transfer rate substantially equal to or less than 1.73Btu/hr-ft-F.
 110. The refrigeration door of claim 104, wherein theinsulating glass unit has a U value substantially equal to or less than0.16 BTU/hr-sq ft-F.
 111. The refrigeration door of claim 104, whereinsaid first sheet or second sheet has an emissivity substantially equalto or less than 0.05.
 112. The refrigeration door of claim 104, whereinthe insulating glass unit has an emissivity substantially equal to orless than 0.04.
 113. The refrigeration door of claim 104, wherein theinsulating glass unit has an emissivity substantially equal to or lessthan 0.01.
 114. The refrigeration door of claim 104, wherein theinterior temperature of the refrigerating compartment is substantiallyequal to or less than minus twenty degrees Fahrenheit; the temperatureof the exterior environment is substantially equal to or greater thanseventy degrees Fahrenheit; and the humidity in the exterior environmentis substantially equal to or greater than sixty percent.
 115. Therefrigeration door of claim 104, wherein the interior temperature of therefrigerating compartment is substantially equal to or less than minusforty degrees Fahrenheit; the temperature of the exterior environment issubstantially equal to or greater than eighty degrees Fahrenheit; andthe humidity in the exterior environment is substantially equal to orgreater than sixty percent.
 116. The refrigeration door of claim 105,wherein said first sealant assembly and said second sealant assemblyeach have a heat transfer rate substantially equal to or less than 1.73Btu/hr-ft-F.
 117. A refrigeration unit including an insulated enclosuredefining a compartment, a cooling system, and a door adapted mounted onan opening of said compartment, said door having an outer surface andcomprising: a first sheet of glass; a second sheet of glass; a firstsealant assembly disposed around the periphery of said first sheet ofglass and said second sheet of glass for maintaining said first sheetand said second sheet in spaced-apart relationship from each other; afirst low emissivity coating adjacent the a surface of said first orsaid second sheet of glass; said first sheet, second sheet, firstsealant assembly, and said first low emissivity coating forming aninsulating glass unit having a U value substantially equal to or lessthan 0.2. BTU/hr-sq ft-F substantially preventing the formation ofcondensation on the outer surface of the door without the application ofelectricity for heating said first surface; and a frame secured aroundthe periphery of said insulating glass unit.
 118. The door of claim 117,further comprising: a third sheet of glass; and a second sealantassembly disposed around the periphery of said second sheet of glass andsaid third of glass for maintaining said second sheet and said thirdsheet in spaced-apart relationship from each other.
 119. Therefrigeration door of claim 117, further comprising: a first chamberdefined by said first sheet of glass, said second sheet of glass, andsaid first sealant assembly; a second chamber defined by said middlesheet of glass, said outer sheet of glass, and said second sealantassembly; and a gas disposed in said first and second chambers.
 120. Therefrigeration door of claim 118, wherein said first sealant assembly andsaid second sealant assembly each have a heat transfer ratesubstantially equal to or less than 1.73 Btu/hr-ft-F.
 121. Therefrigeration door of claim 117, wherein the refrigeration door has anemissivity substantially equal to or less than 0.04.
 122. Therefrigeration door of claim 117, wherein the refrigeration door has anemissivity substantially equal to or less than 0.01.
 123. Therefrigeration door of claim 117, wherein said first sealant assembly hasa heat transfer rate substantially equal to or less than 1.73Btu/hr-ft-F.